1. Technical Field
The present invention relates generally to acoustic transducers. More particularly, the present invention relates to coaxial loudspeaker drivers having independent voice coil elements each being driven by a single magnet.
2. Related Art
Loudspeakers, or acoustic transducers, are universally known and utilized in sound reproduction systems. Essentially, loudspeakers convert electrical energy to acoustic energy according to any one of a variety of well-understood operational principles. Such operational principles are embodied in various designs generally categorized as electrodynamic, electrostatic, piezoelectric, or discharge, among others.
The most common type of loudspeaker is of the electrodynamic variety, in which an electrical signal representative of the specified audio is applied to a voice coil wound around a bobbin and suspended between opposite poles of a magnet. The region between the poles is known as the air gap, and the magnetic field present therein interacts with the electrical signal conducted through the voice coil. The electromagnetic force moves the voice coil, and thus the bobbin, within the air gap, and the displacement or movement thereof is controlled by the magnitude and direction of current in the voice coil and the resulting axial forces. The bobbin is also attached to a cone-shaped semi-rigid diaphragm, and the vibration of the bobbin is correspondingly transferred to the diaphragm. The vibration of the diaphragm causes pressure differences in the surrounding air, thereby producing sound. The base of the diaphragm is flexibly suspended from the rim of the loudspeaker basket, thereby allowing constrained movement while providing lateral stability.
In general, loudspeaker designs aim for faithful re-creation of the sound or acoustic waveform represented by the electrical signal. The typical acoustic waveform is a combination of continuous waveforms of different magnitudes, frequencies, and phases. In this regard, the electrodynamic loudspeaker was characterized by a number of advantages over other designs, including a wide frequency range and efficiency. However, a single loudspeaker cannot reproduce sounds across the entire audible frequency range, due to limitations imposed by weight and size of the diaphragm and bobbin. For instance, while a large diaphragm is capable of handling acoustic waveforms of high magnitudes or louder sounds, its increased weight limits the capability to vibrate at higher frequencies. On the other hand, a small diaphragm is capable of vibrating at higher frequencies, but because of its fragility, higher magnitude waveforms may result in tearing or other damage. Essentially, the size and relative density of the diaphragm are to be configured for a particular frequency range of the acoustic waveform. Although so-called full range loudspeakers have been developed, the response at the peripheral frequencies is less than optimal and results in distortion.
To overcome the above-noted deficiencies, a number of solutions have been proposed for achieving optimal sound reproduction as an alternative to so-called full-range loudspeaker drivers. For example, a standalone system may include more than one loudspeaker driver, each being configured for a particular frequency range. The system may include a tweeter, or loudspeaker driver for high frequency sound reproduction, a midrange driver, and a woofer, or loudspeaker driver for low frequency sound/bass reproduction. It is understood that tweeters have a frequency range of approximately 2,000 to 20,000 Hz, midrange drivers have a frequency range of approximately 300 to 5,000 Hz, and woofers have a frequency range of approximately 40 to 1,000 Hz.
Oftentimes it is undesirable or even impractical to utilize more than one loudspeaker driver in a given installation. In response, loudspeakers having a separate tweeter attached in a co-axial relation to the woofer or midrange driver have been conceived, the earliest example of which is U.S. Pat. No. 2,269,284 to Olson. The Olson device contemplates multiple diaphragms of successive size arranged in a nested, overlapping relationship, with one diaphragm being connected to another with a flexible compliance. The voice coils coupled to the respective one of the diaphragms are also in a nested relation. In response to the complexity associated with the interrelated movement of the diaphragms and voice coils in the Olson device, U.S. Pat. No. 5,295,194 to Christensen contemplates the addition of a tweeter to the voice coil bobbin of the woofer. The tweeter of the Christensen device is piezoelectric, and so is driven independently of the woofer. When the voice coil bobbin of the woofer vibrates at a low frequency, so does the entire tweeter. Thus, one diaphragm is mechanically linked to another.
Alternatively, coaxial loudspeaker devices with drivers that were neither linked mechanically not electrically to the other drivers in the device have been contemplated, such as that disclosed in U.S. Pat. No. 4,552,242 to Kashiwabara. The straightforward solution provided for the stacking of one driver on top of another, with each having its own electromagnetic circuit and diaphragm. However, the Kashiwabara device increased the weight and profile of the loudspeaker.
Accordingly, there is a need in the art for an improved coaxial loudspeaker.